1. Field of the Invention
The present invention relates to marine cargo container transfer devices and particularly to yard tractors utilized to transport cargo containers between yard locations and destinations, such as a location for loading on board ships or on board railway cars or the like.
2. Brief Description of the Prior Art
Yard tractors have long been known that include a driver's cab for hauling a flatbed truck trailer designed to receive a container of cargo which may weigh many tons. The cost of lay time for large cargo ships at the dock is significant, on the order of tens of thousands of dollars per hour or per day, thus rendering efficiency and speed in the transport and loading of the cargo containers of great importance. Typically, such yard tractors have included a cab with a rear doorway so that the driver can exit the driver's seat and access a container or other cargo on the trailer or flatbed. These doorways are typically closed by means of a door slidable along a transverse track and typically latched in either their open or closed position by means of a manual latch including a handle for grasping by the driver. The doors themselves are relatively sturdy and of considerable weight, presenting significant inertia which requires substantial force to slide into the desired position.
The doors typically incorporate a viewing window through which the driver, with his or her head turned, can view any obstacles behind the trailer while backing up or during the loading process or while the container is being loaded on or offloaded from the trailer. Because the mechanical latch handles are typically mounted to the door below the window, this limiting the space available for the window and restricting the driver's view.
Drivers will typically have frequent access to such doors for opening and closing thereof and the doors themselves may have substantial weight, thus affording significant resistance to opening or closing. Accordingly, due to the posture assumed by a driver turning his or her head and neck to view rearwardly while grasping the handle, drivers are placed in a generally compromising position for applying forces which will tend to torque their backs, too often resulting in injury, possible loss of work time for medical attention, and sometimes even incapacitating the driver preventing him or her from serving in his or her driving duties while recovering.
One of the great concerns over operation of heavy equipment in and around yards for storing and moving heavy seagoing cargo containers is the safety of the crane and tractor operators. It is well known that in the workplace, injury very often occurs to the lower back from certain maneuvers that may be undertaken on a day to day basis by a workman such as the driver of a tractor. Lower back movement is a combination of basic flexion, extension and rotation movements. Flexion is when the driver's trunk bends forward and to the side, e.g., leaning over a control or the like and then turning sideways. The rectus, abdominis, internal and external obliques and hip flexors perform these movements. Extension is when the back strains from a bent position or extends from an erect position, e.g., picking up something from the floor of a tractor or reaching for a latch in a lower location within the tractor. The erector spinae, the quadratus, lumborum, in combination with gluteus maximus and hamstrings, perform this movement. Rotation is twisting of the trunk about the waist, e.g., turning to one's side while, for instance, sitting on a driver's seat to reach a control or latch which might be to the rear of the driver's seat. The rectus abdominis, obliques and rector spinae are all involved in rotation movements. These are the basic movements, but the back can move in any combination of these.
For example, reaching up and to the side to grasp a latch is a combination of extension and rotation. Throughout operation of a tractor and performing various functions in opening and closing doors and the like, the back is performing many complex movements involving the muscles in the stomach, hips and low back. What is more, these movements can occur from a sitting position or even a standing position at a steering wheel. For example, sitting at the steering wheel is flexation from a lying and bending down to grasp a latch is flexation from a standing position. It is also important when the back does not move. That is, in performing a maneuver while standing or sitting, it is important that the spine maintain close to ideal posture and alignment. Treatment of injuries resulting various of these maneuvers without proper alignment has led to the recognition of various terms, such as a neutral position, which refers to the low back or lumbar segment of the spine as neither extended nor flexed, with the pelvis flat or not tilted. From this, it can be seen that drivers in a yard tractor required to make maneuvers from the driver's seat which might demand that the driver rotate his or her upper torso and, while so rotated, apply forces such as that which might be necessary to actuate a manual latch and/or slide a rear door between opened and closed positions can lead to unnecessary injury, chronic pain, and even the disability of the driver. It is this problem that stems from the prior art trucks which require latching and unlatching of the rear door by the driver, thereby exposing the driver to such injuries to the lower or mid-back and often resulting in severe medical conditions requiring attention and medical treatment.
In recognition of some of the attendant problems, it has been proposed to provide an air cylinder for assisting in opening and closing of the door. While helpful, such systems still require that the driver turn the neck and shoulders to access the latch for latching the door in its open or closed position, thus applying torque to the lower back and continuing to subject the driver to injury.